Sunday, October 18, 2015

Pumpkins aren't the only orange globes in October. A female Araneus Diadematus in October is typically plump with eggs. Her large, unwieldy size and cooler metabolism-slowing temperatures makes her move slowly compared to her youthful self mere months earlier. At this point, she relies on her sticky silk rather than speed to capture prey.

Chomping on a silverfish that mysteriously fell from the sky

I've talked about the life cycle of the cross spiderbefore. The one most important event I've never documented is how they mate.

Spiders exemplify sexual dimorphism, meaning that males and females have different physical traits, and in many spiders it is so extreme that one could mistakenly conclude that males and females are two different species. While the two sexes of the giant house spider have roughly the same legspan when mature, the females of A. Diadematus are many times the size of the males, such that the male can (and does) often become a snack for the female. (Most notorious for this behaviour (and sexual dimorphism) is the black widow)

Recall what I mentioned in the last post about home advantage - this is clearly the case for A. Diadematus as well. Nearly blind, the male traverses walls, branches, until he finds the threads or webbing of a mature female. He identifies species and readiness to mate by tasting the threads. He coaxes the female out by tapping on a thread of the web, but gently and with a different frequency from an insect in distress. The female approaches the male slowly, but the male must still use caution - the much larger female could at any instant turn on him. His escape strategy is to tie his anchor line further away, so in a panic, all he has to do is let go to swing to safety.

See the male's pedipalps at the front of his head

The male stores his sperm in his pedipalps, the two leglike appendages at the front of his head. He needs to reach the female's seminal receptacle at the underside of her abdomen, which incidentally is also the most vulnerable place to be.

A. Diadematus is the largest and most abundant orb (spiral) web weaver in the Lower Mainland, but nearly 100% of the webs you'd ever see are those of females. Males will start their search for females soon after molting for the last time, and rarely build webs of their own in this last stage (and if they do, they tend to be quite small). Meanwhile, females will continue building webs well after maturity, as they need to gain the nutrition to build up an egg mass.

A. Diadematus is the most easily observed spider (and dare I say, urban wildlife) in the Lower Mainland and many other parts of North America (I've even seen them in the UK and China)...a great starter spider, if you want to learn more about spiders in general, and the micro-ecosystems that surround us. Their entire life cycle is at eye level; their existence targets the only insects in these parts that prey on humans (ie. mosquitos); they don't leave behind messy webs; and they live outdoors which reduces the ick factor. They are one of the last bastions of wilderness that thrive despite humanity.

Wednesday, October 14, 2015

There are few spiders that inspire more fear in this part of the world than the giant house spider.

male

Their gangly legs carry them at record-breaking speeds (1.88km/h according to Guinness World Records) that startle even the calmest humans. Their pedipalps on the males are mistaken as long fangs, and cause frequent misidentification as tarantulas.

Their hairy bodies obscure their segmented bodies, causing fear for what could be hidden beneath. And those beady little eyes.

male

While just about everybody has gotten spooked by one of these running in front of the tv at night, they aren't deserving of such fear.

Despite their fearsome looks, they seldom bite. I've interacted with these spiders for years, and only the appearance of food would cause them to strike (which is hard even for a human to imitate). While some people claim that "they ran straight towards me!", it's much more likely that they ran in a random direction, which happened to be where they were standing. Their beady eyes only sense light/dark, and are incapable of determining the direction of a threat. Their reflex is to run for cover.

male

While they do have fangs, these are usually retracted out of sight. They can only bite what is beneath them, not in front. Their venom is reportedly no worse than a bee or wasp sting.

They build funnel webs, and pretty much stay put their whole lives. The hairs are their body allow them to sense vibrations in the air or their web to give them instant input on what direction prey has landed and how large it is (whether it deserves a hasty retreat, a quick bite and retreat while the prey succumbs, or to grab and hold). Despite living in the dusty corners of most basements, spiders are generally fastidious creatures, staying well groomed to keep their sensitive hairs in their best performance.

The males (pictured above) once mature will seek out females, and these are the ones that typically scare human members of the household into dropping a book on them, or for the more ecologically sensitive, an empty glass.

female

The image above and below is that of a mature female. You'll see the difference in the appearance of pedipalps, which are the short leglike objects to each side of its mouth. In the male, the pedipalps look swollen, because they hold the sperm packets that it intends on using to fertilize the female.

female

Both of the photographed specimens I found in our storage shed, living next to each other. While giant house spiders wouldn't intentionally share webs, sometimes they start out small, but their webs encroach on their neighbours, and they tolerate each other's existence as it's riskier to venture out on their own to seek a new home than to stay put. The enemy you know vs the one you don't...

While many call these hobo spiders (which do have a higher notoriety for their bite toxicity), the ones I photographed do seem to be in fact giant house spiders given their large size (in fact, their large size seems to be the main reason why hobo spiders are, in this part of the word, rarer). Historically, both hobo spiders and giant house spiders were once considered part of the genus Tegenaria, but advances in spider identification resulted in the Giant House Spider split into species Eratigena atrica (the astute would notice that Eratigena is an anagram of Tegenaria) Size of course isn't a reliable indicator of species; more reliable would be examination of the shape of the male pedipalps or the sternum on the female.
While one might think that by their sheer size that these spiders are at the top of their arthropod food chain, wandering males frequently find themselves ensnared by cobweb spiders who are usually only a fraction of the size. Home turf is a huge advantage for web-building spiders.